This invention relates to an electrically heated choke and more particularly to an improved electrically heated choke control circuit and control arrangement.
It is well known that the fuel/air requirements of an internal combustion engine vary in accordance with its temperature. This is particularly true at low temperatures when a richer than normal fuel/air mixture is required than when the engine is heated. In addition, additional fuel flow is required for cold starting. In view of these temperature sensitive fuel/air requirements, it has been the practice to provide internal combustion engines with some form of cold starting and cold running enrichment mechanism with an aim toward providing the proper fuel/air ratio under all running and starting conditions, particularly those where the engine is cold.
One commonly known type of cold starting and cold enrichment mechanism utilizes a choke valve in the induction passage and specifically in the carburetor for restricting the air flow in relation to temperature. When the air flow is restricted, a richer fuel/air mixture will result and the fuel/air mixture can be varied throughout the engine temperature ranges by appropriately controlling the choke valve.
Although the temperature responsive fuel/air requirements of internal combustion engines is well known as is the use for choke valve controlled enrichment, the effectiveness of automatic chokes of the type heretofore proposed has not provided the proper fuel/air ratio for all running conditions and has resulted in poor running or, alternatively, poor fuel economy and high exhaust gas emissions.
More recently it has been proposed to employ electrical heating devices for heating the thermally responsive element that controls the choke valve so as to provide a better control over the fuel/air mixture. Such devices are shown in my U.S. Pat. Nos. 3,699,937 and 3,972,311. Although these devices, which employ positive temperature coefficient heaters for heating the temperature responsive element offer significant advantages over the prior art type of choke mechanisms embodying either exhaust gases or engine coolant as the heating element, they still do not provide the desired degree of choke control under all running conditions. It has been discovered that the most effective choke control and best running can be accomplished if the choke is held closed or substantially closed at a low temperature and then is opened rapidly up to a predetermined position and at a predetermined temperature. When this temperature condition is reached, the continued opening of the choke valve should be maintained at a relatively constant rate until a further predetermined higher temperature is reached. At this temperature, it is desirable to further increase the rate of opening of the choke valve until the engine reaches its operating temperature or a temperature that is relatively close to the normal operating temperature. The types of choke control and heating mechanisms previously proposed simply have not been able to achieve this type of temperature choke position relationship.
It is, therefore, a principal object of this invention to provide an improved choke mechanism for an internal combustion engine.
It is a yet further object of this invention to provide an improved electrically heated choke.
It is a still further object of this invention to provide an improved control mechanism for controlling the current supplied to an electrically heated choke.